1. Field of the Invention
The invention relates in general to a communication system, and more particularly to a communication system which includes a wireless fidelity (WiFi) system and a worldwide interoperability for microwave access (WiMAX) system and can operate simultaneously under the WiFi system and the WiMAX system.
2. Description of the Related Art
The WiFi system and the WiMAX system are both very popular communication systems nowadays. The WiFi system is widely applied to local area network (LAN) with a bandwidth about 2.4 GHz˜2.5 GHz. Limited by the size of an area, the WiFi system is mostly used for providing an internet service in a small area, such as hotspots in some fast food shops. The WiMAX system is widely applied to metropolitan area network (MAN) with a bandwidth about 2.3 GHz˜2.4 GHz and 2.5 GHz˜2.7 GHz and mainly used in a login circuit for connecting an internet service. That is, it replaces the present digital subscriber line (DSL) to provide a wireless broadband login service at the last mile. The WiFi system and the WiMAX system have a complementary relationship.
In the present notebook computer or hand-held device, the antenna structure applied to a WiFi system is normally a structure of multi-input and multi-output (MIMO), such as having two transmission terminals and three reception terminals (2×3) or three transmission terminals and three reception terminals (3×3). The antenna structure applied to the WiMAX system is normally a structure of single-input and multi-output (SIMO) or MIMO, such as having one transmission terminal and two reception terminals (1×2) or two transmission terminals and two reception terminals (2×2). Referring to FIG. 1, a schematic diagram of a conventional communication system is shown. A communication system 100, which is applied to a notebook computer or a hand-held device, includes a WiFi device 110, a WiMAX device 120, antennas 131˜136, filters 141˜146 and a microprocessor 150. The WiFi device 110 is a WiFi card and the WiMAX device 120 is a WiMAX card. Besides, for the purpose extension, the filter 145 is denoted by a dash line.
Due to control of the microprocessor 150 and isolation effects of the filters 141˜143, the WiFi device 110 will receive the WiFi signal WF but not the WiMAX signal WM from the antennas 131˜133. By the same reason, due to control of the microprocessor 150 and the isolation effects of the filters 144˜146, the WiMAX device 120 will receive the WiMAX signal WM but not the WiFi signals WF from the antennas 134˜136.
The notebook computer or hand-held device applies the above communication system 110 and antenna structure for the purpose of power saving and volume reduction. However, the above communication system 110 and antenna structure cannot effectively integrate the WiFi system and the WiMAX system and have to use two corresponding antenna structures, which may largely increase the cost without reducing the size and weight of the notebook computer or hand-held device. Besides, some notebook computers or hand-held devices may use a method of changing cards for the above two systems. However, the method of changing cards is to set the communication system in usage to be the WiFi system or the WiMAX system before the notebook computer or hand-held device leaves the factory. Therefore, although the volume of the notebook computer or hand-held device can be reduced, only one single system can be used at a time and this will reduce the convenience of using the WiFi system or WiMAX system simultaneously.